Art of cracking hydrocarbons



, May 29, 1934. E. w. ISOM ART OF CRACKING HYDROCARBONS Filed April 14,1931 (bade/merfrarf/aoa #0 Tower Vapor Separaflng Recap fa c/e ATTORNEYSPatented May 29, 1934 UNETED STATES ART OF CRACKING HYDROCARBONS EdwardW. Isom, Sear sdale, N. Y., assigncr to Sinclair Refining Company, NewYork, N. Y., a

corporation of Maine Application April 14,

4 Claims.

This invention relates toimprovements in the production of lower boilingoils, such as gasoline, from higher boiling oils, such as crude oil,topped crude oil, flux oil and the like. The invention relatesparticularly to improvements in operations, carried out for thispurpose, to which a dirty higher boiling stock is supplied and in whicha clean higher boiling stock separated from the dirty higher boilingstock in the operation is heated after separation from the dirty stockto a high cracking temperature and in which vaporized components of bothstocks are together subjected to a refluxing operation for theseparation of the desired product or products and the clean stock to beheated in the operation to a high cracking temperature.

According to the present invention, the refluxing operation in which theseparation of the desired product or products from the clean stock to beheated to a high cracking temperature is effected is controlled bypassing reflux condensate from this refluxing operation in heat exchangewith the vapors therein after cooling this reflux condensate by heatexchange with the dirty stock supplied to the operation, the dirty stockbeing concurrently preheated by this heat exchange.

' direct or indirect or both. Important advantages with respect to heateconomy and with respect to control of the operation, among others, arethus secured without involving any contact between or intermixture ofthe dirty stock or any part of it and the vapors or any part of them orany condensate separated therefrom inthe refluxing operation.

The invention will be further described in. connection with theaccompanying drawing which illustrates, diagrammatically andconventionally, one form of apparatus adapted for carrying out theinvention. It is intended and will be understood that this more detaileddescription of the invention is for the purpose of illustration. Theinvention can be carried out in other and different forms of apparatus.

The apparatus illustrated in the accompanying drawing comprises twoheating conduits 1 and 2 arranged in separate heating furnaces 3 and 4respectively, a vapor separating receptacle 5, a fractionating tower 6,a heat exchanger 7, a condenser 8 and receiver 9, a cooler 10, and pumps11, 1'2 and 13. The heating furnaces 3 and 4 maybe of any preferredconstruction and 1931, Serial No. 529,978

arrangement. The vapor separating receptacle 5 may be externallyunheated but thermally in-, sulated to minimize heat loss. Thefractionatirig tower 6 may be of any preferred construction,conventional bubble tower construction for example. This tower also maybe thermally insulated to minimize heat loss. Pump 12 may be of anypreferred type of hot oil pump. Any of the conventional forms may beused for the other elements of the apparatus.

In carrying out the invention in the apparatus illustrated in theaccompanying drawing, a stream of residual stock, suppliedthrough'connection 14, is forced successively through the heat exchanger'7 and the heating conduit 1' into the vapor separating receptacle 5 bymeans oi pump 11 and in the heating conduit 1 is heated to atemperature, for example, approximating 650850 F., a stream ofdistillate stock supplied through connection 15 or connections 15 and 16is forced through the heating conduit 2 into the vapor separatingreceptacle '5 by means of pump 12 andin the heating conduit 2 is heatedto a temperature, for example, approximating 900- 1050" F., vapors aretaken off from the vapor sep-' arating receptacle 5 through connection17 and in the fractionating tower 6 are subjected to a refluxingoperation, one or more lower boiling products being taken off throughconnections 18, or 18 and 19, reflux condensate being supplied from thefractionating tower'6 to the heating conduit 2 through connection 15,and the refluxing operation is controlled, although not necessarilyexclusively so, by heat exchange between the vapors in the refluxingoperation and. reflux condensate returned to the refluxing operationthrough connection 20 after passing through the heat exchanger '7 inwhich the reflux condensate passing therethrough is cooled by heatexchange with theresidual stock supplied through connection 14.

Although the severe cracking effected in carrying out the operation inthe apparatus illustrated is eiiected entirely in the heating conduit 2,some cracking may be effected in the'heating conduit 1. However, ingeneral it is advantageous to limit the temperature to which the dirtystock supplied to the heating conduit 1 is heated therein to atemperature below which no substantial cracking of components of thisstock occurs.

The residual stock supplied to the heating conduit 1 may be suppliedthereto under a pressure just suflicient to force it therethrough intothe vapor separating receptacle 5 orit may be supplied under a somewhathigher pressure and this margin of pressure released as the hot oilproducts from the heating conduit 1 are discharged into the vaporseparating receptacle 5. Similarly, the distillate stock supplied to theheating conduit 2 may be supplied thereto under a pressure justsufficient to force it therethrough into the vapor separating receptacle5 or it may be supplied under a higher pressure and this margin ofpressure released as the hot oil products from the heating conduit 2 aredischarged into the vapor separating receptacle 5. The vapor separatingreceptacle 5 may be operated under a pressure, for example, in theneighborhood of atmospheric pressure or under a higher pressure, 100-150pounds per square inch for example. The discharge pressure from theheating conduit 1 may exceed that prevailing in the vapor sepa ratingreceptacle 5 by as much as 100-200 pounds per square inch for example,and the discharge pressure from the heating conduit 2 may exceed thatprevailing in the vapor separating receptacle 5 by as much as 500-800pounds per square inch for example. Valves 21 and 22 are provided formaintaining any desired differential between the discharge pressure fromthe heating conduit 1 and the pressure prevailing in the vaporseparating receptacle 5, and valve 23 is provided for maintaining anydesired differential between the discharge pressure from the heatingconduit 2 and the pressure prevailing in the vapor separating receptacle5. The two streams of hot oil products discharged from the heatingconduits 1 and 2 may be introduced into the vapor separating receptacle5 at separate points or the hot oil products discharged from the heatingconduit 1 may be introduced into the hotter oil products discharged fromthe heating conduit 2 before the latter are introduced into the vaporseparating receptacle 5 to assist in checking overcracking of componentsof the latter. Residual tar is discharged from the vapor separatingreceptacle 5 through connection 24.

The reflux condensate supplied to the heating conduit 2 throughconnection is a distillate stock, or clean stock, having been separatedas vapors from unvaporized constituents in the vapor separatingreceptacle 5 and condensed in the fractionating tower 6. Additionalquantities of similar distillate stocks, or clean stocks, such as gasoil character or kerosene character fractions may be supplied throughconnection 16. The residual stocks supplied through connection 14embrace crude oil stocks, topped crude oil stocks, flux oil stocks, tarsfrom pressure distillation cracking operations, and similar dirtystocks.

The heating furnace 3 as illustrated is ar ranged to providecountercurrent heat exchange between the heating gases and the stockpassing through the heating conduit 1, the stock thus being heated to atemperature progressing gradually to the maximum attained. The heatingfurnace 4 as illustrated is arranged to provide concurrent heat exchangebetween the heating gases and the stock passing through the heatingconduit 2, thus making it possible to bring the stockto a hightemperature approximating the maximum attained more or less quickly andto maintain it at this temperature or at a temperature graduallyincreasing from this temperature to the maximum attained for a longer orshorter period of time in the heating conduit by controlling the rate offiring of the furnace with respect to the rate of circulation of thestock through the heating conduit.

The cooled reflux condensate used for controlling the refluxingoperation carried out in the frac-tionating tower 6 returned throughconnection may comprise all or a part forced through the heat exchanger7 by means of the pump 12, the valve 25 being closed and the other partbeing supplied to the heating conduit 2, or all of the reflux condensatemay be forced through the heat exchanger '7 and part returned throughconnection 20 and part supplied to the heating conduit 2 through valves26 and 25 respectively, valve 27 being closed, or part of the refluxcondensate may be supplied to the heating conduit 2 without passingthrough heat exchanger 7 through valve 2'? and part of the refluxcondensate forced through the heat exchanger '7, this latter part beingagain divided by means of valves 25 and 26.

The cooled reflux condensate returned through connection 20 forcontrolling the refluxing operation may be introduced into thefractionating tower 6 through connection 28, in direct heat exchangewith the vapors in the refluxing operation, or it may be circulatedthrough the cooling coil 29 in the upper end of the fractionating tower6 in indirect heat exchange with the vapors in the refluxing operation,and then either introduced into the fractionating tower 6 throughconnection 28 or discharged into connection 15 through connection 30. Itwill be appreciated that valved connection 31 and valved connection 32may be closed completely in such operations or that either or both ofthese connections may be opened as by-passes to an extent regulated toassist in controlling the refluxing operation. A single product,gasoline for example, may be taken off as vapors through connection 18or one or more additional products, kerosene and light gas oil forexample, may be taken oi as condensates through connection 19 orcorresponding connections. Uncondensed vapors and gases are separated inthe receiver 9, the condensed product, gasoline for example, beingdischarged through connection 33 and uncondensed vapors and gasesthrough connection 34. Control of ios lit

the refluxing operation in the fractionating tower 6 may be supplementedby the return through heated to a temperature of 750 F. as dischargedfrom the heating coil 1. The discharge pressure of coil 1 may bemaintained at approximately 200 pounds per square inch. Condensate fromthe bottom of the fractionating tower 6, having a gravity of 28-32 Baum,advantageously may be heated to a temperature of 975980 F. as dischargedfrom heating coil 2, while maintaining a discharge pressure of 700-750pounds per square inch thereon. The pressure in the vapor separatingreceptacle advantageously may be reduced to 35-50 pounds per squareinch. Condensate withdrawn from the bottom of fractionating tower 6 at atemperature of approximately 625 F. may be cooled to about 225 F. byheat exchange with the dirty stock in heat exchanger 7. Condensatecooled in this manner may be turned to the upper end of thefractionating towerin quantities regulated to maintain the tem- Baumegravity topped crude advantageously may be perature of the vapor mixturein the upper end of this tower at about 380 F.

In operations in which an overhead product is taken off as vapors, asthrough connection 18, and an additional condensate product is takenoil, as through connection 19, the arrangement of apparatus illustratedis particularly advantageous in providing for control of the refluxingoperation in the upper part of the fractionating tower by indirect heatexchange between the vapors and the refluxing medium in this region andproviding for control of the refluxing operation in the lower part ofthe fractionating tower, below the point at which the additionalcondensate product is taken off, by means of direct heat exchangebetween the vapors and the refluxing medium in this region.

I claim:

1. In the production of lower boiling hydrocarbon oils from higherboiling hydrocarbon oils, the improvement which comprises forcing aresidual siock in a confined stream through a heating zone and thencedirectly into a vapor sepa rating receptacle, heating said stream ofresidual stock in said heating zone to at least an incipient crackintemperature at which its lower boiling components will vaporize, forcinga distillate stock in a confined stream through a second heating zoneand thence directly into said vapor separating receptacle, heating saidstream of distillate stock to a high cracking temperature in said secondheating zone, taking off vapors from said vapor separating receptacleand subjecting them to a refluxing operation, supplying refluxcondensate from said refluxing operation to said second heating zone,controlling said refluxing operation while passing reflux condensatefrom said refluxing operation in countercurrent indirect heat exchangewith said stream of residual stock on its way to said first mentionedheating zone, thereby cooling the former, and passing the thus cooledcondensate in heat exchange with the vapors in the said refluxingoperation.

2. In the production of lower boiling hydrocarbon oils from higherboiling hydrocarbon oils, the improvement which comprises forcing aresidual stock in a confined stream through a heating zone and thencedirectly into a vapor separating receptacle, heating said stream ofresidual stock in said heating zone to an incipient cracking temperatureat which its lower boiling components will vaporize but at which nosubstantial cracking of its components occurs, forcing a distillatestock in a confined stream through a second heating zone and thencedirectly into said vapor separating receptacle, heating said stream ofdistillate stock to a high cracking temperature in said second heatingzone, taking ofi vapors from said vapor separating receptacle andsubjecting them to a refluxing operation, supplying reflux condensatefrom said refluxing operation to said second heating zone, controllingsaid refluxing operation by passing reflux condensate from saidrefluxing operation in countercurrent indirect heat exchange with saidstream of residual stock on its way to said first mentioned heatingzone, thereby cooling the former, and passing the thus cooled condensatein heat exchange with the vapors in the said refluxing operation.

3. In the production of lower boiling hydrocarbon oils from higherboiling hydrocarbon oils, the improvement which comprises forcing aresidual stock in a confined stream through a heating zone and thencedirectly into a vapor separating receptacle, heating said stream ofresidual stock in said heating zone to at least an incipient crackingtemperature at which its lower boiling components will vaporize, forcinga distillate stock in a confined stream through a second heating zoneand thence directly into said vapor separating receptacle, heating saidstream of distillate stock to a high cracking temperature in said secondheating zone, taking off vapors from said vapor separating receptacleand subjecting them to a refluxing operation, supplying refluxcondensate from said refluxing operation to said second heating zone,controlling said refluxing operation by passing reflux condensate fromsaid refluxing operation in countercurrent indirect heat exchange withsaid stream of residual stock on its way to said first mentioned heatingzone, thereby cooling the former, and passing the thus cooled condensatein direct heat exchange with the vapors in the said refluxing operation.

4. In the production of lower boiling hydrocarbon oils from higherboiling hydrocarbon oils, the improvement which comprises forcing aresidual stock in a confined stream through a heating zone and thencedirectly into a vapor separating receptacle, heating said stream ofresidual stock in said heating zone to at least an incipient crackingtemperature at which its lower boiling components will vaporize, forcinga distillate stock in a confined stream through a second heating zoneand thence directly into said vapor separating receptacle, heating saidstream of distillate stock to a high cracking temperature in said secondheating zone, taking oii vapors from said vapor separating receptacleand subjecting them to a refluxing operation, supplying refluxcondensate from said refluxing-operation to said second heating zone,controlling said refluxing operation by passing reflux condensate from'said refluxing operation in countercurrent indirect heat exchange withsaid stream of residual stock on its way to its first mentioned heatingzone, thereby cooling the former, and passing the thus cooled condensatein indirect heat exchange with the vapors in the said refluxingoperation.

EDWARD W. ISOM.

